The present invention relates to a flap assembly adapted for use as a trailing edge flap of the wing of an airplane. More particularly, the present invention relates to a flap assembly having capabilities for short take-off and landing aircraft and a variety of other mission requirements.
It is quite common for present commercial aircraft to have single, double or triple slotted flaps that travel in curved tracks. While this arrangement does provide for optimum flap positions for take-off and landing with only small, low-drag fairings, the flap track supports are heavy and have inherent in-service problems with track wear and jamming. The main problem arises from the line contact of the highly loaded aft roller on the track. Another arrangement appears in the Boeing 747 airplane, where there is a single slotted flap mounted on an overhead four-bar linkage.
Some short to medium range airplanes are equipped with double slotted flaps, mounted from a simple hinge below the wing. This flap configuration is designed to provide very high lift coefficients for landing, with take-off lift coefficient and lift-to-drag ratio not being critical. In this particular airplane configuration, the cruise drag of the deep flap support fairings is not too important for the short-range mission.
There is need for improvement for mission requirements where there is relatively high gross weight, high altitude, and limited runway length in that there should be an adequately high lift-to-drag ratio for take-off. For a mix of mission requirements, short and long range, with high gross weight and intermediate runway length, intermediate gross weight and short field length, a flap system with the aerodynamic characteristics of the track guided flaps is desirable. Thus, there is still a need for a flap system having the desirable features of the track guided flaps, while alleviating some of the difficulties associated with such track guided flaps.
To determine the sort of flap arrangement needed, consideration should be given to three basic mission requirements. First, there is the consideration of the length of the landing field and touch down speed limits of the airplane. This condition becomes the flap sizing criteria on short to medium range airplanes with high wing loading for operation from short runways, including short take-off and landing airplanes (i.e., STOL airplanes). The flap position for landing is the fully extended position for maximum lift coefficient.
The next consideration is the take-off field length limit. This infludences the choice of flap assembly configuration particularly where there is high thrust to weight ratio airplanes with a requirement for very short take-off field length.
A third consideration is the one-engine-out second segment climb gradient. This condition will generally determine the flap configuration for take-off on twin and three engine airplanes with high wing loading. In order to achieve the minimum climb gradient with one engine failed the airplane lift-to-drag ration has to be optimized. High lift-to-drag ratios can be achieved with high Fowler motion at low flap angles. Since the flap setting for take-off and second segment climb is usually the same, the take-off flap setting is influenced by both take-off field length (the second consideration noted above) and second segment climb gradient.
With regard to the flap motion from stowed to fully deployed position, there are of course a variety of mechanisms in the prior art. As long as the intermediate flap positions are not critical, the criteria for selecting the mechanism are generally simplicity (with low cost and low risk), low load (low weight) and small size (with the resulting low drag). However, where there are rather stringent requirements for take-off field length limit and also the one-engine-out second segment climb gradient, the intermediate positions of the flap are quite critical. Airplanes which are take-off climb gradient critical need a flap system that provides very high Fowler motion at low flap angles, with most of the flap rotation occurring toward the end of deployment of the flap.
Thus, consideration has been given to achieving a flap assembly configuration which provides adequate fowler motion with relatively small flap deflection, while requiring only a small flap support fairing with low cruise drag. It is an object of the present invention to provide such a flap assembly, with a desirable mix of advantageous features such as those discussed above.
A search of the patent literature has disclosed a number of patents showing various flap configurations and means for deploying the flaps. Typical of these are the following:
U.S. Pat. No. 2,352,062, Zap, discloses a trailing edge flap configuration showing flaps not only employing a simple hinge, but also circular arc tracks. In some configurations, these are used separately, and in others, the two are combined, with the track itself being hinged mounted.
U.S. Pat. No. 2,502,315, Erhart, discloses a trailing edge flap configuration where there are two slideways of a particular configuration to which a flap is mounted.
U.S. Pat. No. 2,542,792, Bennett et al, has a trailing edge flap hinged mounted to a rear portion of the aircraft. There is an intermediate flap which is deployed above and forwardly of the main hinge mounted flap.
U.S. Pat. No. 2,556,326, Grant, also shows a hinge mounted trailing edge flap. Further, there is an intermediate flap which has a stowed and a deployed position.
U.S. Pat. No. 2,661,166, Gordon, illustrates a trailing edge flap pivotally mounted to one link which is in turn pivotally connected to a second link that is pivotally mounted to stationary structure. There is a third link, pivotally connected to the trailing edge flap, and also having a pivot connection to a slide-mounted member. The second and third links are interconnected at a pivot point.
U.S. Pat. No. 2,779,555, Danielson, discloses a trailing edge flap arrangement where two links are pivotally connected by first ends of the flap. Opposite ends of the links are mounted in a slideway, with differential movement of the links being provided by two chain drives. This causes the flap to tilt as it moves closer to its rear position.
U.S. Pat. No. 2,974,903, Chomart, shows a trailing edge flap mounted to a stationary track positioned at the elevation of the flap. The forward end of the flap is pivotally connected to a link that is forward of the slideway and pivotally connected by an upper end to stationary structure.
U.S. Pat. No. 3,223,356, Alvarez-Calderon, shows an arrangement of hinge mounted flaps.
U.S. Pat. No. 3,438,598, Tammel, has a trailing edge flap having two support points thereon, each of which is mounted in a respective track. The tracks are arranged so that as the flap moves to its aft position, it is deflected downwardly.
U.S. Pat. No. 3,478,988, Roed, shows trailing edge flaps with a hinge mounting.
U.S. Pat. No. 3,568,957, Wood, discloses a trailing edge flap supported on a curved track at one point. It is also supported from a nut member traveling on a fixedly mounted screw conveyor.
U.S. Pat. No. 3,583,660, Hurkamp, shows a trailing edge flap having several configurations. In one configuration, the flap is supported at one point in a curved track, and by a link having its rear end attached to the rear of the flap, and its forward end secured to stationary structure at a location forward of the track.
U.S. Pat. No. 3,767,140, Johnson, shows a two-flap configuration. The aft flap operates in a slideway of the fore flap, and the fore flap is operated by a linkage system.
British Pat. No. 560,996 discloses a trailing edge flap movable from a stowed position to a rearward deployed position. While the mounting arrangement of this flap is not clearly disclosed, the test of this patent indicates that it is mounted from rails.